CN114175387A - Isolating membrane, electrochemical device comprising same and electronic device - Google Patents

Isolating membrane, electrochemical device comprising same and electronic device Download PDF

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Publication number
CN114175387A
CN114175387A CN202180004689.3A CN202180004689A CN114175387A CN 114175387 A CN114175387 A CN 114175387A CN 202180004689 A CN202180004689 A CN 202180004689A CN 114175387 A CN114175387 A CN 114175387A
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coating
coating layer
secondary particles
separator
particles
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CN114175387B (en
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樊晓贺
魏增斌
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Ningde Amperex Technology Ltd
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Ningde Amperex Technology Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
    • H01M50/457—Separators, membranes or diaphragms characterised by the material having a layered structure comprising three or more layers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/403—Manufacturing processes of separators, membranes or diaphragms
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
    • H01M50/417—Polyolefins
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
    • H01M50/42—Acrylic resins
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
    • H01M50/426—Fluorocarbon polymers
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/431—Inorganic material
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/431—Inorganic material
    • H01M50/434—Ceramics
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    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/443—Particulate material
    • H—ELECTRICITY
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    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/446—Composite material consisting of a mixture of organic and inorganic materials
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
    • H01M50/451—Separators, membranes or diaphragms characterised by the material having a layered structure comprising layers of only organic material and layers containing inorganic material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

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  • Electrochemistry (AREA)
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  • Engineering & Computer Science (AREA)
  • Inorganic Chemistry (AREA)
  • Manufacturing & Machinery (AREA)
  • Ceramic Engineering (AREA)
  • Materials Engineering (AREA)
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  • Secondary Cells (AREA)
  • Cell Separators (AREA)

Abstract

The application provides a barrier film and electrochemical device and electronic device containing the barrier film, wherein the barrier film comprises a barrier film substrate, and a first coating and a second coating which are respectively arranged on two surfaces of the barrier film substrate, the first coating comprises secondary polymer particles, and the melting point of the secondary particles is 130-150 ℃. The first coating in the isolating membrane has good bonding performance and electrolyte swelling resistance, and more gaps are formed inside the secondary particles, so that electrolyte can enter the isolating membrane, the electrolyte wettability of the first coating is improved, and the electrochemical device has better low-temperature performance.

Description

Isolating membrane, electrochemical device comprising same and electronic device
Technical Field
The application relates to the field of electrochemistry, in particular to a separation film, an electrochemical device comprising the separation film and an electronic device comprising the separation film.
Background
The lithium ion battery has the characteristics of large specific energy, high working voltage, low self-discharge rate, small volume, light weight and the like, and is widely applied to various fields of electric energy storage, portable electronic equipment, electric automobiles and the like.
With the rapid development of the application of lithium ion batteries in the fields of electric vehicles and the like, the defect that the low-temperature performance of the lithium ion batteries is difficult to adapt to the low-temperature environment is more and more obvious. Under low temperature conditions, the performance of the lithium ion battery, such as the effective discharge capacity, is obviously reduced, and the application of the lithium ion battery is restricted, so that the low temperature performance of the lithium ion battery needs to be improved urgently.
Disclosure of Invention
An object of the present application is to provide a separator, and an electrochemical device and an electronic device including the same, to improve low-temperature performance of a lithium ion battery. The specific technical scheme is as follows:
a first aspect of the present application provides a separation film comprising a separation film substrate, and a first coating layer and a second coating layer respectively disposed on both surfaces of the separation film substrate;
wherein the first coating comprises secondary polymer particles, and the melting point of the secondary particles is 130-150 ℃.
In the following description of the present application, the present application is explained by taking a lithium ion battery as an example of an electrochemical device, but the electrochemical device of the present application is not limited to a lithium ion battery.
The first coating layer and the second coating layer in the present application may be respectively disposed on both surfaces of the release film substrate. The polymer secondary particles in the first coating can be formed by aggregating the primary particles, so that more gaps are formed in the secondary particles, and the electrolyte can easily permeate into the gaps, thereby being beneficial to improving the electrolyte wettability of the first coating.
The melting point of the polymer secondary particles in the present application is 130 ℃ to 150 ℃. Without being bound by any theory, when the melting point of the secondary particles is too high, for example, higher than 150 ℃, it is not favorable for the improvement of the adhesive property of the first coating layer; when the melting point of the secondary particles is too low, for example, below 130 ℃, the polymer is liable to be excessively swollen and even dissolved in the electrolyte, which also results in a decrease in the adhesion property of the first coating layer and deteriorates the dynamic properties of the lithium ion battery. By controlling the melting point of the secondary particles of the present invention within the above range, a first coating layer having a low degree of swelling and good adhesion can be obtained.
The second coating layer in this application contains a polymer, which may be selected from high molecular weight polymers.
In one embodiment of the present application, Dv50 of the primary particles forming the above secondary particles is between 50nm and 1000nm, and the above primary particles may be polymer particles. Without being limited to any theory, when the Dv50 of the primary particles is too small, for example, less than 50nm, the secondary particles are formed with less voids inside, and the electrolyte is less likely to penetrate into the voids, which is not favorable for the improvement of the electrolyte wettability of the first coating layer; when the Dv50 of the primary particles is too large, the primary particles are less likely to agglomerate to form secondary particles, and the electrolyte wettability of the first coating layer is also affected. By controlling the Dv50 of the primary particles of the present invention within the above range, a first coating layer having good wettability and adhesion can be obtained.
In one embodiment of the present application, the Dv50 of the secondary particles is from 10 μm to 30 μm. Without being bound by any theory, when the Dv50 of the secondary particles is too small, e.g., less than 10 μm, the secondary particles are more likely to agglomerate, affecting the dynamic performance of the lithium ion battery; when the Dv50 of the secondary particles is too large, for example, more than 30 μm, the cohesive force of the secondary particles is easily decreased, which is not favorable for improving the cohesive property of the first coating layer, and affects the energy density of the lithium ion battery. By controlling the Dv50 of the secondary particles of the present application within the above range, a first coating layer having good adhesion can be obtained.
In one embodiment of the present application, the secondary particles have a sphericity of 0.7 to 1. Without being bound by any theory, when the sphericity of the secondary particles is too low, for example, less than 0.7, the secondary particles are more likely to cover the surface of the separation film substrate, hinder lithium ion transport, and affect the kinetic performance of the lithium ion battery. By controlling the sphericity of the secondary particles of the present application within the above range, a first coating layer having good adhesion can be obtained.
In one embodiment of the present application, the secondary particles have a crystallinity of 38% to 46%. Without being limited to any theory, when the crystallinity of the secondary particles is too low, for example, less than 38%, the swelling degree of the secondary particles increases, easily blocking voids in the separation film substrate, hindering lithium ion transmission, affecting the dynamic performance of the lithium ion battery; when the crystallinity of the secondary particles is too high, for example, higher than 46%, the melting point of the secondary particles is too high, so that the cohesive force of the secondary particles is lowered, which is not favorable for improving the cohesive property of the first coating layer. By controlling the crystallinity of the secondary particles of the present invention within the above range, a first coating layer having good adhesion can be obtained.
In one embodiment of the present application, the first coating has a coat weight of 0.4g/m2To 1.0g/m2The coating weight of the second coating layer was 0.1g/m2To 1g/m2. Without being limited to any theory, when the coating weight of the first coating layer or the second coating layer is too low, the interfacial adhesion is insufficient and the coating adhesion property is degraded; when the coating weight of the first coating layer or the second coating layer is too high, the relative content of the electrode active material in the lithium ion battery is reduced, and the effect is reducedAnd the energy density of the lithium ion battery. By controlling the coating weight of the first coating and/or the second coating of the secondary particles in the range, the good interfacial bonding property between the isolating membrane and the electrode plate can be realized, and the relative content of the electrode active material in the lithium ion battery can be improved, so that the energy density of the lithium ion battery is improved.
In one embodiment of the present application, the thickness of the first coating layer is from 5 μm to 20 μm; the second coating layer has a thickness of 0.2 to 4 μm. Without being limited to any theory, when the thickness of the first coating layer or the second coating layer is too low, the interfacial adhesion is insufficient and the coating adhesion property is degraded; when the thickness of the first coating layer or the second coating layer is too high, the relative content of the electrode active material in the lithium ion battery decreases, affecting the energy density of the lithium ion battery. By controlling the thickness of the first coating and/or the second coating of the secondary particles in the range, the interface bonding performance between the isolating membrane and the electrode plate is good, and the relative content of the electrode active material in the lithium ion battery can be improved, so that the energy density of the lithium ion battery is improved.
In one embodiment of the present application, in order to provide better adhesion between the secondary particles and the release film substrate, an auxiliary binder may be included in the first coating layer to serve as auxiliary adhesion, the mass of the auxiliary binder is 5 wt% to 15 wt% of the total mass of the first coating layer, and the secondary particles are 85 wt% to 95 wt% of the total mass of the first coating layer. The content of the auxiliary binder should not be too low or too high, and too low affects the binding ability between the secondary particles, and too high affects the binding performance of the first coating due to the decrease in the content of the secondary particles.
The secondary particles of the present application may include at least one of homopolymers or copolymers of vinylidene fluoride, hexafluoropropylene, ethylene, propylene, vinyl chloride, chloropropene, acrylic acid, acrylates, styrene, butadiene, and acrylonitrile.
In the present application, the kind of the high molecular polymer in the second coating layer is not particularly limited as long as the object of the present application can be achieved, and for example, the high molecular polymer may be selected from at least one of homopolymers or copolymers of methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, ethylene, styrene, chlorostyrene, fluorostyrene, methylstyrene, acrylic acid, methacrylic acid, methacrylonitrile, and maleic acid.
In one embodiment, the second coating layer comprises a core-shell structure high molecular polymer, the core main component can be a polymer, and the polymer can be a homopolymer obtained by polymerizing one polymerizable monomer or a copolymer obtained by polymerizing two or more polymerizable monomers. Specifically, the core of the high molecular polymer having a core-shell structure is selected from at least one of homopolymers or copolymers of ethyl acrylate, butyl acrylate, ethyl methacrylate, styrene, chlorostyrene, fluorostyrene, methylstyrene, acrylic acid, methacrylic acid, and maleic acid.
The shell of the core-shell polymer binder may be a homopolymer of one polymerizable monomer or a copolymer of two or more polymerizable monomers selected from acrylates, aromatic monovinyl compounds and vinyl cyanated compounds. Specifically, the shell of the high molecular polymer with the core-shell structure is selected from at least one of homopolymers or copolymers of methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, ethylene, chlorostyrene, fluorostyrene, methyl styrene, acrylonitrile and methacrylonitrile.
In one embodiment of the present application, the second coating layer comprises a non-core-shell structured high molecular polymer selected from at least one of homopolymers or copolymers of acrylic acid, acrylate, butadiene, styrene, acrylonitrile, ethylene, chlorostyrene, fluorostyrene, or propylene.
In one embodiment of the present application, the second coating may also contain a thickener, an auxiliary binder, and a wetting agent. The thickener is used for improving the stability of the slurry and preventing the slurry from settling. The thickener is not particularly limited in the present application as long as the object of the present invention can be achieved, and may be, for example, sodium carboxymethylcellulose. The auxiliary binder functions as an auxiliary binder to further improve the adhesive property of the second coating layer, and the application is not particularly limited as long as the object of the application is achieved, and for example, the auxiliary binder may include at least one of homopolymers or copolymers of ethyl acrylate, butyl acrylate, ethyl methacrylate, styrene, chlorostyrene, fluorostyrene, methylstyrene, acrylic acid, methacrylic acid, maleic acid, acrylonitrile, or butadiene. The wetting agent functions to reduce the surface energy of the slurry and prevent coating skip, and is not particularly limited as long as the object of the present application can be achieved, and for example, the wetting agent may include at least one of dimethylsiloxane, polyethylene oxide, an oxyethylene alkylphenol ether, a polyoxyethylene fatty alcohol ether, a polyoxyethylene polyoxypropylene block copolymer, or dioctyl sodium sulfosuccinate.
In one embodiment of the present application, the polymer is contained in an amount of 78 to 87.5% by mass, the auxiliary binder is contained in an amount of 5 to 10% by mass, the thickener is contained in an amount of 0.5 to 2% by mass, and the wetting agent is contained in an amount of 7 to 10% by mass, based on the total mass of the second coating layer, so that the second coating layer having excellent adhesion properties can be obtained.
In one embodiment of the present application, an inorganic coating layer may be further disposed between the first coating layer and the separation film substrate, or an inorganic coating layer may be disposed between the first coating layer and the separation film substrate and between the second coating layer and the separation film substrate, or an inorganic coating layer may be disposed between the second coating layer and the separation film substrate, and both of the above-mentioned disposing methods can further improve the mechanical strength of the separation film.
In one embodiment of the present application, the thickness of the inorganic coating is 0.5 μm to 6 μm, and not limited to any theory, when the thickness of the inorganic coating is too low, for example, less than 0.5 μm, the mechanical strength of the separator decreases, which is not favorable for improving the cycle performance of the lithium ion battery; when the thickness of the inorganic coating is too high, for example, more than 6 μm, the separator becomes thick as a whole, and the relative content of the electrode active material decreases, which is not favorable for increasing the energy density of the lithium ion battery. By controlling the thickness of the inorganic coating within the above range, the cycle performance and energy density of the lithium ion battery can be improved.
The material of the inorganic coating layer is not particularly limited as long as the object of the present application can be achieved, and for example, at least one of boehmite, magnesium hydroxide, alumina, titania, silica, zirconia, tin dioxide, magnesia, zinc oxide, barium sulfate, boron nitride, aluminum nitride, or silicon nitride may be contained in the inorganic coating layer. The method for producing the inorganic coating layer is not particularly limited, and the inorganic coating layer can be formed by applying a slurry containing the inorganic material to the surface of the separator substrate.
In this application, can have the one side and the positive pole piece contact of first coating with the barrier film, have the one side and the negative pole piece contact of second coating with the barrier film, make all have good bonding effect between barrier film and positive pole piece and the negative pole piece, and have better electrolyte infiltration nature between barrier film and the positive pole piece to improve lithium ion battery's low temperature cycle performance and quick charge cycle performance. The separator of the present application has lithium ion permeability and electron barrier properties.
The positive electrode sheet in the present application is not particularly limited as long as the object of the present application can be achieved. For example, the positive electrode tab generally includes a positive electrode current collector and a positive electrode active material layer. The positive electrode current collector is not particularly limited, and may be any positive electrode current collector in the art, such as an aluminum foil, an aluminum alloy foil, or a composite current collector. The positive electrode active material layer includes a positive electrode active material, the positive electrode active material is not particularly limited, and any positive electrode active material in the art may be used, and for example, may include at least one of lithium nickel cobalt manganese oxide (811, 622, 523, 111), lithium nickel cobalt aluminate, lithium iron phosphate, a lithium rich manganese-based material, lithium cobalt oxide, lithium manganese iron phosphate, or lithium titanate.
The negative electrode sheet in the present application is not particularly limited as long as the object of the present application can be achieved. For example, the negative electrode tab generally includes a negative electrode current collector and a negative electrode active material layer. Among them, the negative electrode collector is not particularly limited, and any negative electrode collector in the art, such as copper foil, aluminum alloy foil, and composite collector, etc., may be used. The anode active material layer includes an anode active material, and the anode active material is not particularly limited, and any anode active material in the art may be used. For example, at least one of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon, hard carbon, silicon carbon, lithium titanate, and the like may be included.
The lithium ion battery of the present application further includes an electrolyte, which may be one or more of a gel electrolyte, a solid electrolyte, and an electrolyte including a lithium salt and a non-aqueous solvent.
In some embodiments herein, the lithium salt is selected from LiPF6、LiBF4、LiAsF6、LiClO4、LiB(C6H5)4、LiCH3SO3、LiCF3SO3、LiN(SO2CF3)2、LiC(SO2CF3)3、LiSiF6One or more of LiBOB and lithium difluoroborate. For example, the lithium salt may be LiPF6Since it can give high ionic conductivity and improve cycle characteristics.
The non-aqueous solvent may be a carbonate compound, a carboxylate compound, an ether compound, other organic solvent, or a combination thereof.
The carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, a fluoro carbonate compound, or a combination thereof.
Examples of the above chain carbonate compound are dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), Methyl Propyl Carbonate (MPC), Ethyl Propyl Carbonate (EPC), Methyl Ethyl Carbonate (MEC), and combinations thereof. Examples of the cyclic carbonate compound are Ethylene Carbonate (EC), Propylene Carbonate (PC), Butylene Carbonate (BC), Vinyl Ethylene Carbonate (VEC), and combinations thereof. Examples of the fluoro carbonate compound are fluoroethylene carbonate (FEC), 1, 2-difluoroethylene carbonate, 1, 2-trifluoroethylene carbonate, 1,2, 2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1, 2-difluoro-1-methylethylene carbonate, 1, 2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, and combinations thereof.
Examples of the above carboxylic acid ester compounds are methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ -butyrolactone, decalactone, valerolactone, mevalonolactone, caprolactone, and combinations thereof.
Examples of the above ether compounds are dibutyl ether, tetraglyme, diglyme, 1, 2-dimethoxyethane, 1, 2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof.
Examples of such other organic solvents are dimethylsulfoxide, 1, 2-dioxolane, sulfolane, methyl sulfolane, 1, 3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters and combinations thereof.
The application also provides an electrochemical device, which comprises a positive pole piece, a negative pole piece and an isolating membrane, wherein the isolating membrane is positioned between the positive pole piece and the negative pole piece, and has good low-temperature performance.
The present application also provides an electronic device comprising the electrochemical device described in the embodiments of the present application, having good low temperature performance.
The electronic device of the present application is not particularly limited, and may be any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable facsimile machine, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a handheld cleaner, a portable CD player, a mini-disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power source, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a lighting fixture, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a large household battery, a lithium ion capacitor, and the like.
The process for preparing the electrochemical device is well known to those skilled in the art, and the present application is not particularly limited. For example, a lithium ion battery can be manufactured by the following process: the positive electrode and the negative electrode are overlapped through a separation film, and are placed into a shell after being wound, folded and the like according to needs, electrolyte is injected into the shell and the shell is sealed, wherein the separation film is the separation film provided by the application. In addition, an overcurrent prevention element, a guide plate, or the like may be placed in the case as necessary to prevent a pressure rise or overcharge/discharge inside the lithium ion battery.
The method for producing the primary polymer particles of the present application is not particularly limited, and a production method by a person skilled in the art can be employed, and for example, the following production methods can be employed:
vacuumizing the reaction kettle, after nitrogen is pumped to replace oxygen, adding deionized water, vinylidene fluoride (VDF), emulsifier perfluoroalkyl carboxylate and chain transfer agent isopropanol into the reaction kettle containing a stirrer until the pressure of the reaction kettle is about 3.5 MPa. And then heating to 50-70 ℃, starting polymerization reaction at the rotating speed of the stirrer of 70-100 r/min, continuously adding vinylidene fluoride monomer, keeping the pressure of the reaction kettle at 3.5MPa until the solid content of the emulsion in the reactor reaches 25-30%, stopping the reaction, recovering unreacted monomer, discharging the polymer emulsion, centrifuging, washing and drying to obtain the primary polymer particles.
The initiator is not particularly limited as long as it can initiate polymerization of the monomer, and may be, for example, diisopropylbenzene hydroperoxide. The addition amounts of the monomer, the deionized water, the initiator and the chain transfer agent are not particularly limited, as long as the added monomer is ensured to perform a polymerization reaction, for example, the deionized water is 5 times to 10 times of the mass of the monomer, the initiator accounts for 0.05% to 0.5% of the mass of the monomer, the emulsifier accounts for 0.1% to 1% of the mass of the monomer, and the chain transfer agent accounts for 3% to 7% of the mass of the monomer.
The preparation method of the auxiliary binder is not particularly limited, and a preparation method commonly used by those skilled in the art may be used, and is selected according to the kind of the monomer used, for example, a solution method, a slurry method, a gas phase method, and the like.
The method for preparing the secondary particles is not particularly limited, and a method for preparing the secondary particles by those skilled in the art may be used, for example, the primary particles may be prepared by an emulsion polymerization method, and the slurry containing the primary particles may be spray-dried to obtain the secondary particles. Of course, the polymerization of the primary particles may be carried out by various conventional polymerization methods, for example, emulsion polymerization, suspension polymerization, etc., as long as the secondary particles can be obtained from the primary particles to achieve the object of the present invention.
In the present application, the term "Dv 50" denotes the particle size with a cumulative distribution of particles of 50%, i.e. the volume content of particles smaller than this particle size is 50% of the total particles.
The application provides a barrier film and contain electrochemical device and electron device of this barrier film, because contain polymer secondary particle in the first coating of this barrier film, the melting point of this secondary particle is 130 ℃ to 150 ℃, make first coating have good adhesive property and anti electrolyte swelling performance, and the secondary particle is inside to have more space, more do benefit to electrolyte and get into wherein, thereby improve the electrolyte infiltration nature of first coating, make lithium ion battery have better low temperature performance.
Drawings
In order to illustrate the technical solutions of the present application and the prior art more clearly, the following briefly introduces examples and figures that need to be used in the prior art, it being obvious that the figures in the following description are only some examples of the present application.
FIG. 1 is a schematic structural view of a separator according to a first embodiment of the present application;
FIG. 2 is a schematic structural view of a separator according to a second embodiment of the present application;
FIG. 3 is a schematic structural view of a separator according to a third embodiment of the present application;
fig. 4 is a schematic structural view of a separator according to a fourth embodiment of the present application.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is further described in detail below with reference to the accompanying drawings and examples. It is to be understood that the embodiments described are only a few embodiments of the present application and not all embodiments.
As shown in fig. 1, the separation film of the present application includes a separation film substrate 1, and a first coating layer 2 and a second coating layer 3 respectively disposed on both surfaces of the separation film substrate 1, wherein the first coating layer 2 includes polymer secondary particles 4, and the secondary particles 4 are formed by aggregating primary particles 41.
In one embodiment of the present application, as shown in fig. 2, an inorganic coating layer 5 is disposed between the first coating layer 2 and the release film substrate 1.
In one embodiment of the present application, as shown in fig. 3, an inorganic coating layer 5 is disposed between the first coating layer 2 and the separation film substrate 1, and an inorganic coating layer 5 is also disposed between the second coating layer 3 and the separation film substrate 1.
In one embodiment of the present application, as shown in fig. 4, an inorganic coating layer 5 is disposed between the second coating layer 2 and the release film substrate 1.
Examples
Hereinafter, embodiments of the present application will be described in more detail with reference to examples and comparative examples. Various tests and evaluations were carried out according to the following methods. Unless otherwise specified, "part" and "%" are based on mass.
The test method and the test equipment are as follows:
and (3) testing the adhesive force between the isolating film and the electrode plate:
adopting national standard GB/T2790-: cutting the compounded sample into strips of 15mm multiplied by 54.2mm at the temperature of 85 ℃, the pressure of 1Mpa and the hot pressing time of 85s (seconds), and testing the adhesive force between the isolating membrane and the positive pole piece or the negative pole piece according to a 180-degree stripping test standard.
And (3) low-temperature performance test:
step 1: and (3) carrying out first charging and discharging on the formed lithium ion battery in an environment of 25 ℃: charging at constant current and constant voltage under the charging current of 0.1C until the upper limit voltage is 4.45V, and standing the fully charged lithium ion battery for 5 minutes;
step 2: discharging to 3V at a rate of 0.2C, recording the discharge capacity of the first circulation, and standing for 5 minutes;
and 4, step 4: constant-current charging is carried out to 4.45V at a charging rate of 1.5C, constant-voltage charging is carried out to 0.02C, and then standing is carried out for 5 minutes;
and 5: adjusting the furnace temperature to {25,10,0, -10, -20,45,60}, standing for 5 minutes, discharging to 3V at 0.2C magnification, and standing for 5 minutes;
step 6: adjusting the temperature of the furnace to 25 ℃, and standing the lithium ion battery for 60 minutes;
and 7: and (4) circulating the steps from the step 4 to the step 6, sequentially testing the temperature conditions according to the temperature conditions in the step 5, sequentially recording the final discharge capacity of the lithium ion battery under the temperature conditions, then selecting the final discharge capacity of the lithium ion battery recorded under the temperature condition of minus 20 ℃, and calculating the low-temperature capacity retention rate of the lithium ion battery under the temperature condition of minus 20 ℃ by using the following expression:
the low-temperature capacity retention ratio (— final discharge capacity of the lithium ion battery at 20 ℃ per discharge capacity of the lithium ion battery at 25 ℃ in the first cycle) × 100%.
Melting point test of the polymer secondary particles:
using a general type Differential Scanning Calorimeter (DSC) method: weighing 5mg of polymer secondary particle samples, heating to 150 ℃ at the heating rate of 5 ℃/min, collecting DSC curves, and determining the melting points of the polymer secondary particles according to the obtained DSC curves.
Crystallinity test of polymer secondary particles:
using a general-purpose Differential Scanning Calorimeter (DSC), a predetermined amount of a sample of secondary particles (e.g., 5mg) of a polymer is heated to 180 ℃ at a constant rate (e.g., 5 ℃/min), the temperature is maintained for 2min, and then the temperature is reduced to 80 ℃ at a constant rate (e.g., 5 ℃/min), and the crystallinity obtained by the DSC method is determined by the following formula:
degree of crystallinity Δ Hm/ΔHm 0
In the formula,. DELTA.Hm、ΔHm 0The heat of fusion of the sample and the heat of fusion of the fully crystallized sample, respectively.
Dv50 test for primary polymer particles, secondary polymer particles:
the Dv50 of the primary polymer particles and the secondary polymer particles were measured using a laser particle sizer.
Examples
Hereinafter, embodiments of the present application will be described in more detail with reference to examples and comparative examples. Various tests and evaluations were carried out according to the following methods. Unless otherwise specified, "part" and "%" are based on mass.
Example 1
<1-1. production of copolymer Secondary particles >
<1-1-1. preparation of Primary particles >
Vacuumizing the reaction kettle, after nitrogen is pumped for replacing oxygen, adding deionized water, vinylidene fluoride, initiator diisopropylbenzene hydroperoxide, emulsifier perfluoroalkyl carboxylate and chain transfer agent isopropanol into the reaction kettle containing a stirrer until the pressure of the reaction kettle is 3.5MPa, wherein the deionized water is 7 times of the mass of the vinylidene fluoride monomer, the initiator accounts for 0.2 percent of the mass of the vinylidene fluoride monomer, the emulsifier accounts for 0.5 percent of the mass of the vinylidene fluoride monomer, and the chain transfer agent accounts for 5 percent of the mass of the vinylidene fluoride monomer. And then heating to 60 ℃, rotating the stirrer at a speed of 80r/min, starting polymerization, continuously adding the vinylidene fluoride monomer, keeping the pressure of the reaction kettle at 3.5MPa, stopping the reaction until the solid content of the emulsion in the reactor reaches 25%, recovering unreacted monomer, discharging the polymer emulsion, centrifuging, washing and drying to obtain the primary polyvinylidene fluoride particles.
<1-1-2. preparation of Secondary particles >
Dispersing primary polyvinylidene fluoride particles into deionized water, and stirring for 120 minutes by using an MSK-SFM-10 vacuum stirrer at a revolution speed of 40rpm and a rotation speed of 1500rpm to obtain primary particle slurry with the solid content of 10%;
and transferring the primary particle slurry to a centrifugal turntable spray head of a spray drying granulator, wherein the centrifugal rotating speed is 2000rpm, and forming tiny fog drops. And cooling and collecting powder to obtain the polyvinylidene fluoride secondary particles, wherein the inlet temperature of the spray drying granulator is 110 ℃, the outlet temperature of the spray drying granulator is 100 ℃. The obtained secondary particles had a melting point of 130 ℃, a Dv50 of 20 μm and a sphericity of 0.8.
<1-2. preparation of Positive electrode sheet >
Mixing the positive active material lithium cobaltate, acetylene black and polyvinylidene fluoride (PVDF) according to the mass ratio of 94: 3, adding N-methylpyrrolidone (NMP) as a solvent, preparing slurry with the solid content of 75%, and uniformly stirring. And uniformly coating the slurry on one surface of an aluminum foil with the thickness of 12 mu m, drying at 90 ℃, cold-pressing to obtain a positive pole piece with the thickness of a positive active material layer of 100 mu m, and repeating the steps on the other surface of the positive pole piece to obtain the positive pole piece with the positive active material layer coated on two surfaces. Cutting the positive pole piece into the specification of 74mm multiplied by 867mm, and welding the pole lugs for later use.
<1-3. preparation of negative electrode sheet >
Mixing the negative active material artificial graphite, acetylene black, styrene butadiene rubber and sodium carboxymethylcellulose according to the mass ratio of 96: 1: 1.5, adding deionized water as a solvent, preparing slurry with the solid content of 70%, and uniformly stirring. And uniformly coating the slurry on one surface of a copper foil with the thickness of 8 mu m, drying at 110 ℃, cold-pressing to obtain a negative pole piece with the negative active material layer of 150 mu m in thickness and with the single-surface coated with the negative active material layer, and repeating the coating steps on the other surface of the negative pole piece to obtain the negative pole piece with the double-surface coated with the negative active material layer. Cutting the negative pole piece into a size of 74mm multiplied by 867mm, and welding a pole lug for later use.
<1-4. preparation of separator >
<1-4-1. first coating preparation >
Adding 90g of prepared polyvinylidene fluoride secondary particles into a stirrer, adding 10g of auxiliary binder acrylonitrile, stirring and mixing uniformly, adding deionized water, stirring, adjusting the viscosity of the slurry to be 100mPa & s, and adjusting the solid content to be 12% to obtain slurry A; the slurry A was uniformly coated on one side of the PE release film substrate to obtain a first coating layer having a coating weight of 0.8g/m as shown in Table 12And finishing drying in an oven. Wherein, the base material of the isolation film is PE material with the thickness of 5 μm.
<1-4-2. preparation of second coating layer >
Adding 91g of polymer binder with a non-core-shell structure (copolymer polymerized by 80 mass percent of styrene, 10 mass percent of isobutyl acrylate and 10 mass percent of acrylonitrile, and the Dv50 is 0.3 mu m) into a stirrer, adding 0.5g of sodium carboxymethylcellulose, and uniformly stirring and mixing; adding 8.5g of wetting agent dimethyl siloxane, then adding deionized water, stirring, adjusting the viscosity of the slurry to 40mPa & s, and adjusting the solid content to 5% to obtain slurry B. Uniformly coating the slurry B on the other surface of the PE release film substrate to obtain a second coating layer, wherein the coating weight of the second coating layer is 0.5g/m2And finishing drying in an oven.
<1-5 > preparation of electrolyte solution >
Mixing non-aqueous organic solvents of Ethylene Carbonate (EC), diethyl carbonate (DEC), Propylene Carbonate (PC), Propyl Propionate (PP) and Vinylene Carbonate (VC) according to a mass ratio of 20: 30: 20: 28: 2 in an environment with water content less than 10ppm, and then adding lithium hexafluorophosphate (LiPF) to the non-aqueous organic solvent6) Dissolving and mixing uniformly to obtain electrolyte, wherein the LiPF is6The mass ratio of the organic solvent to the non-aqueous organic solvent is 8: 92.
<1-6 preparation of lithium ion Battery >
And (3) sequentially stacking the prepared positive pole piece, the prepared isolating membrane and the prepared negative pole piece, contacting one surface of the isolating membrane with the first coating with the positive pole piece, contacting one surface of the isolating membrane with the second coating with the negative pole piece, and winding to obtain the electrode assembly. And (3) putting the electrode assembly into an aluminum-plastic film packaging bag, dehydrating at 80 ℃, injecting the prepared electrolyte, and performing vacuum packaging, standing, formation, shaping and other processes to obtain the lithium ion battery.
Example 2
Using a method similar to the preparation of the (1-1) copolymer secondary particles in example 1, polyvinylidene fluoride secondary particles having a melting point, Dv50, sphericity and crystallinity as shown in Table 1 were prepared.
Example 3
Using a method similar to the preparation of the (1-1) copolymer secondary particles in example 1, polyvinylidene fluoride secondary particles having a melting point, Dv50, sphericity and crystallinity as shown in Table 1 were prepared.
Example 4
Using a method similar to the preparation of the (1-1) copolymer secondary particles in example 1, polyvinylidene fluoride secondary particles having a melting point, Dv50, sphericity and crystallinity as shown in Table 1 were prepared.
Example 5
Using a method similar to the preparation of the (1-1) copolymer secondary particles in example 1, polyvinylidene fluoride secondary particles having a melting point, Dv50, sphericity and crystallinity as shown in Table 1 were prepared.
Example 6
Using a method similar to the preparation of the (1-1) copolymer secondary particles in example 1, polyvinylidene fluoride secondary particles having a melting point, Dv50, sphericity and crystallinity as shown in Table 1 were prepared.
Example 7
Using a method similar to the preparation of the (1-1) copolymer secondary particles in example 1, polyvinylidene fluoride secondary particles having a melting point, Dv50, sphericity and crystallinity as shown in Table 1 were prepared.
Example 8
Using a method similar to the preparation of the (1-1) copolymer secondary particles in example 1, polyvinylidene fluoride secondary particles having a melting point, Dv50, sphericity and crystallinity as shown in Table 1 were prepared.
Example 9
Using a method similar to the preparation of the (1-1) copolymer secondary particles in example 1, polyvinylidene fluoride secondary particles having a melting point, Dv50, sphericity and crystallinity as shown in Table 1 were prepared.
Example 10
Using a method similar to the preparation of the (1-1) copolymer secondary particles in example 1, polyvinylidene fluoride secondary particles having a melting point, Dv50, sphericity and crystallinity as shown in Table 1 were prepared.
Example 11
Using a method similar to the preparation of the (1-1) copolymer secondary particles in example 1, polyvinylidene fluoride secondary particles having a melting point, Dv50, sphericity and crystallinity as shown in Table 1 were prepared.
Example 12
Using a method similar to the preparation of the (1-1) copolymer secondary particles in example 1, polyvinylidene fluoride secondary particles having a melting point, Dv50, sphericity and crystallinity as shown in Table 1 were prepared.
Example 13
Using a method similar to the preparation of the (1-1) copolymer secondary particles in example 1, polyvinylidene fluoride secondary particles having a melting point, Dv50, sphericity and crystallinity as shown in Table 1 were prepared, and the coating amount of the first coating layer as shown in Table 1.
Example 14
Using a method similar to the preparation of the (1-1) copolymer secondary particles in example 1, polyvinylidene fluoride secondary particles having a melting point, Dv50, sphericity and crystallinity as shown in Table 1 were prepared, and the coating amount of the first coating layer as shown in Table 1.
Example 15
Using a method similar to the preparation of the (1-1) copolymer secondary particles in example 1, polyvinylidene fluoride secondary particles having a melting point, Dv50, sphericity and crystallinity as shown in Table 1 were prepared, and the coating amount of the first coating layer as shown in Table 1.
Example 16
Using a method similar to the preparation of the (1-1) copolymer secondary particles in example 1, polyvinylidene fluoride secondary particles having a melting point, Dv50, sphericity and crystallinity as shown in Table 1 were prepared, and the coating amount of the first coating layer as shown in Table 1.
Example 17
Polyvinylidene fluoride secondary particles having Dv50, sphericity and crystallinity as shown in table 2 were prepared in a similar manner to the preparation of (1-1) copolymer secondary particles in example 1.
Example 18
Polyvinylidene fluoride secondary particles having Dv50, sphericity and crystallinity as shown in table 2 were prepared in a similar manner to the preparation of (1-1) copolymer secondary particles in example 1.
Example 19
Except that in the preparation of the (1-4-2) second coating preparation, the coating weight of the second coating was adjusted to 0.1g/m2Except for this, the adhesion between the separator and the negative electrode sheet was as shown in table 3 in the same manner as in example 1.
Example 20
Except that in the preparation of the (1-4-2) second coating preparation, the coating weight of the second coating was adjusted to 1.0g/m2Except for this, the adhesion between the separator and the negative electrode sheet was as shown in table 3 in the same manner as in example 1.
Example 21
The procedure of example 3 was repeated, except that in the production of the (1-6) lithium ion battery, the side of the separator having the first coating layer was brought into contact with the negative electrode sheet, and the side of the separator having the second coating layer was brought into contact with the positive electrode sheet. The adhesion between the separator and the positive and negative electrode sheets, respectively, is shown in table 4.
Example 22
The same as example 3 was repeated, except that in example 3, the polyvinylidene fluoride secondary particles of the first coating layer were replaced with copolymer secondary particles of 95% by mass of vinylidene fluoride and 5% by mass of hexafluoropropylene.
Example 23
The same as example 3, except that in example 3, the polyvinylidene fluoride secondary particles of the first coating layer were replaced with copolymer secondary particles having a mass fraction of 85% of styrene, 10% of butadiene and 5% of acrylic acid.
Example 24
The same as example 3 was repeated, except that in example 3, the polyvinylidene fluoride secondary particles of the first coating layer were replaced with copolymer secondary particles having a mass fraction of 75% styrene and 25% acrylic acid ester.
Example 25
The same as example 3 except that the polyvinylidene fluoride secondary particles of the first coating layer in example 3 were replaced with copolymer secondary particles having a mass fraction of 50% acrylic acid, 25% acrylonitrile and 25% styrene.
Example 26
The same as example 3 was performed, except that in the preparation of the (1-4) separator, an inorganic coating layer was disposed between the first coating layer and the separator substrate as shown in fig. 2. The thickness of the inorganic coating was 2 μm.
< preparation of inorganic coating layer >
Inorganic particle boehmite having a Dv50 of 1 μm was mixed with polyacrylate in a mass ratio of 90: 10 and dissolved in deionized water to form an inorganic coating slurry having a solid content of 50%, and the resulting inorganic coating slurry was uniformly coated on one side of a separator substrate by a dimple coating method to obtain a heat-resistant layer, and drying was completed in an oven. Then, a first coating layer was prepared on the surface of the inorganic coating layer in accordance with < preparation of first coating layer > of example 1.
Example 27
The same as example 3 was performed, except that in the preparation of the (1-4) separator, the inorganic coating layer was disposed between the first coating layer and the separator substrate, and between the second coating layer and the separator substrate as shown in fig. 3. The thickness of the inorganic coating was 2 μm.
Example 28
The same as example 3, except that in the preparation of the (1-4) separator, an inorganic coating layer was disposed between the second coating layer and the separator substrate as shown in fig. 4. The thickness of the inorganic coating was 2 μm.
Comparative example 1
Polyvinylidene fluoride secondary particles were prepared in a similar manner to the preparation of (1-1) copolymer secondary particles in example 1, adjusted to have a melting point of 125 ℃ and a crystallinity of 34, and the rest was the same as in example 3.
Comparative example 2
Polyvinylidene fluoride secondary particles were prepared in a similar manner to the preparation of (1-1) copolymer secondary particles in example 1, adjusted to have a melting point of 155 ℃ and a crystallinity of 50, and the rest was the same as in example 3.
Comparative example 3
Polyvinylidene fluoride secondary particles were prepared in a similar manner to the preparation of (1-1) copolymer secondary particles in example 1, adjusted to have a Dv50 of 5 μm, and the rest was the same as in example 3.
Comparative example 4
Polyvinylidene fluoride secondary particles were prepared in a similar manner to the preparation of (1-1) copolymer secondary particles in example 1, adjusted to have a Dv50 of 35 μm, and the rest was the same as in example 3.
Comparative example 5
Polyvinylidene fluoride secondary particles were prepared in a similar manner to the preparation of (1-1) copolymer secondary particles in example 1, adjusted to have a sphericity of 0.5, and the rest was the same as in example 3.
Comparative example 6
Except that the coating amount of the first coating layer was adjusted to 0.3g/m in the preparation of the (1-4) separator2Otherwise, the same procedure as in example 3 was repeated.
Comparative example 7
Except that the coating amount of the first coating layer was adjusted to 1.1g/m in the preparation of the (1-4) separator2Otherwise, the same procedure as in example 3 was repeated.
Comparative example 8
The same as example 3, except that the first coating layer was replaced with the second coating layer in the preparation of the (1-4) separator, that is, both surfaces of the separator were coated with the second coating layer.
The preparation parameters and test results of the respective examples and comparative examples are shown in the following tables 1 to 6:
Figure BDA0003484881240000181
Figure BDA0003484881240000191
Figure BDA0003484881240000201
as can be seen from examples 1 to 5 and comparative examples 1 to 2 in table 1, as the melting point of the secondary particles increases, the adhesion between the separator and the positive electrode sheet tends to decrease, and the low-temperature capacity retention rate of the lithium ion battery generally tends to increase. However, when the melting point of the secondary particles is too low (e.g., comparative example 1), the low-temperature capacity retention rate of the lithium ion battery is affected, and when the melting point of the secondary particles is too high (e.g., comparative example 2), the adhesion between the separator and the electrode tab is affected.
As can be seen from examples 6 to 9 and comparative examples 3 to 4 in table 1, as the secondary particles Dv50 increased, the adhesion between the separator and the positive electrode sheet tended to decrease, and the low-temperature capacity retention rate of the lithium ion battery tended to increase. However, when Dv50 of the secondary particles is too small (e.g., comparative example 3), it affects the low-temperature capacity retention rate of the lithium ion battery, and when Dv50 of the secondary particles is too large (e.g., comparative example 4), it affects the adhesion between the separator and the electrode tab.
As can be seen from examples 10 to 12 and comparative example 5 in table 1, as the sphericity of the secondary particles increases, the adhesion between the separator and the positive electrode sheet tends to decrease, and the low-temperature capacity retention rate of the lithium ion battery tends to increase. But when the sphericity of the secondary particles is too small (e.g., comparative example 5) affects the low-temperature capacity retention rate of the lithium ion battery.
As can be seen from examples 13 to 16 and comparative examples 6 to 7 in table 1, as the coating amount of the first coating layer increases, the adhesion between the separator and the positive electrode sheet tends to increase, the low-temperature capacity retention rate of the lithium ion battery tends to decrease, when the coating amount of the first coating layer is too small (e.g., comparative example 6) affects the adhesion between the separator and the electrode sheet, and when the coating amount of the first coating layer is too large (e.g., comparative example 7) affects the low-temperature capacity retention rate of the lithium ion battery, which may be due to a decrease in the relative content of the electrode active material although the increase in the coating amount of the first coating layer can increase the interfacial adhesion.
As can be seen from table 1, example 3 and comparative example 8, when both surfaces of the separator were the second coating layers, the low-temperature capacity retention rate was affected although the separator had a high adhesive force with the positive electrode tab.
As can be seen from examples 3, 17 to 18 and comparative examples 1 to 2 in table 2, as the crystallinity of the secondary particles increases, the adhesion between the separator and the positive electrode sheet tends to decrease, and the low-temperature capacity retention rate of the lithium ion battery generally tends to increase. However, when the crystallinity of the secondary particles is too low (e.g., comparative example 1), the low-temperature capacity retention rate of the lithium ion battery is affected, and when the crystallinity of the secondary particles is too high (e.g., comparative example 2), the adhesive force between the separator and the electrode tab is affected.
As can be seen from examples 3, 19 to 20 in table 3, as the coating amount of the second coating increases, the adhesion between the separator and the negative electrode tab also tends to increase, which indicates that the second coating of the present application can also improve the adhesion between the interfaces, but the low-temperature capacity retention rate of the lithium ion battery is not greatly improved, which may be related to the electrolyte wettability of the second coating.
As can be seen from table 4, in examples 3 and 21, after the contact surfaces of the separator and the positive and negative electrode plates are exchanged, the interfacial adhesion and the low-temperature capacity retention rate of the lithium ion battery are not changed much, which indicates that the first coating of the present application has good adhesion performance to both the positive electrode plate and the negative electrode plate, and good electrolyte wettability.
As can be seen from examples 22 to 25 in Table 5, when different polymer secondary particles are used in the first coating layer, the adhesion between the polymer secondary particles and the electrode plate is similar, and the low-temperature capacity retention rate of the prepared lithium ion battery is close.
As can be seen from examples 26 to 28 of table 6, the inorganic coating layer does not greatly affect the interfacial adhesion property and the low-temperature capacity retention rate of the lithium ion battery. However, the mechanical strength of the separator can be improved by providing an inorganic coating.
In conclusion, the isolating membrane with the first coating and the second coating can effectively improve the bonding performance between the isolating membrane and the motor pole piece and obtain the low-temperature performance of the battery.
The above description is only exemplary of the present application and should not be taken as limiting the present application, as any modification, equivalent replacement, or improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims (14)

1. An isolation film comprises an isolation film substrate, and a first coating and a second coating which are respectively arranged on two surfaces of the isolation film substrate;
wherein the first coating comprises secondary polymer particles, and the melting point of the secondary particles is 130-150 ℃.
2. The separator of claim 1, wherein the first coating has at least one of the following characteristics:
a) the Dv50 of the primary particles forming the secondary particles is from 50nm to 1000 nm;
b) the secondary particles have a Dv50 of 10 to 30 μm;
c) the secondary particles have a sphericity of 0.7 to 1;
d) the secondary particles have a crystallinity of 38% to 46%.
3. The separator of claim 1, wherein the first coating has a coat weight of 0.4g/m2To 1.0g/m2(ii) a The coating weight of the second coating layer is 0.1g/m2To 1g/m2。
4. The separator of claim 1, wherein the first coating has a thickness of 5 to 20 μ ι η; the second coating layer has a thickness of 0.2 to 4 μm.
5. The separator of claim 1, wherein the first coating further comprises an auxiliary binder, and the auxiliary binder accounts for 5 wt% to 15 wt% of the total mass of the first coating.
6. The separator of claim 1, wherein the secondary particles comprise at least one of homopolymers or copolymers of vinylidene fluoride, hexafluoropropylene, ethylene, propylene, vinyl chloride, chloropropene, acrylic acid, acrylates, styrene, butadiene, and acrylonitrile.
7. The separator of claim 1, wherein the second coating layer comprises a core-shell structured high molecular polymer, the core of which is selected from at least one of homopolymers or copolymers of ethyl acrylate, butyl acrylate, ethyl methacrylate, styrene, chlorostyrene, fluorostyrene, methylstyrene, acrylic acid, methacrylic acid, and maleic acid; the shell of the high molecular polymer with the core-shell structure is selected from at least one of homopolymers or copolymers of methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, ethylene, chlorostyrene, fluorostyrene, methyl styrene, acrylonitrile and methacrylonitrile.
8. The separator of claim 1, wherein the second coating layer comprises a non-core-shell structured high molecular polymer selected from at least one of homopolymers or copolymers of acrylic acid, acrylate, butadiene, styrene, acrylonitrile, ethylene, chlorostyrene, fluorostyrene, or propylene.
9. The release film according to claim 1, wherein the second coating layer further contains a thickener, an auxiliary binder, and a wetting agent, and the polymer is contained in an amount of 78% to 87.5% by mass, the auxiliary binder is contained in an amount of 5% to 10% by mass, the thickener is contained in an amount of 0.5% to 2% by mass, and the wetting agent is contained in an amount of 7% to 10% by mass, based on the total mass of the second coating layer.
10. The release film according to claim 1, wherein an inorganic coating layer is further provided between the first coating layer and the release film substrate and/or between the second coating layer and the release film substrate, the inorganic coating layer having a thickness of 0.5 to 6 μm.
11. The separator of claim 10, wherein the inorganic coating comprises at least one of boehmite, magnesium hydroxide, alumina, titania, silica, zirconia, tin dioxide, magnesia, zinc oxide, barium sulfate, boron nitride, aluminum nitride, or silicon nitride.
12. The separator of claim 5 or 9, wherein the auxiliary binder comprises at least one of homopolymers or copolymers of ethyl acrylate, butyl acrylate, ethyl methacrylate, styrene, chlorostyrene, fluorostyrene, methylstyrene, acrylic acid, methacrylic acid, maleic acid, acrylonitrile, and butadiene.
13. An electrochemical device comprising the separator of any one of claims 1-12.
14. An electronic device comprising the electrochemical device of claim 13.
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